Glass ceramics with quartz-like crystals are already known from the state of the art. They are usually glass ceramics with so-called high quartz mixed crystals. These crystals contain different additional ions in the SiO2 framework silicate, which allow this particular type of crystal to have a metastable existence even at room temperature. If these ions were not contained in the glass ceramic, the high quartz formed at high temperatures in the glass ceramic would change into low quartz at 573° C. Holand and Beall describe that glass ceramics with crystals in the high quartz structure have the particular property of low thermal expansion or even of zero expansion within a large temperature range (“Glass-Ceramic Technology” 2nd edition, Wiley, 2012, 272-273). For such glass ceramics, linear coefficients of thermal expansion (CTE) of less than 1.5·10−6 K−1 (within the temperature range of 20 to 700° C.) are usually measured. Even glass ceramics with a negative coefficient of expansion can be provided with the aid of the high quartz structure.
Further, lithium disilicate glass ceramics are known from EP 0 916 625 A1, which contain lithium disilicate as main crystal phase and, because of their high translucence and very good mechanical properties, are used particularly in the dental field and primarily for the preparation of crowns and bridges.
From W. Buchalla, “Comparative Fluorescence Spectroscopy Shows Differences in Non-Cavitated Enamel Lesions”, Caries Res. 2005, 39, 150-156, it is known that natural teeth display a bluish-white fluorescence with wavelengths in the range of from 400 to 650 nm under ultraviolet light.
Rukmani et al., J. Am. Ceram. Soc. 2007, 90, 706-711, describe the influence of V and Mn colorants on the crystallization behaviour and the optical properties of Ce-doped lithium disilicate glass ceramics. To prepare the glass ceramics, a mixture of the starting materials SiO2, ZrO2, Li2CO3, K2CO3, MgCO3 and Al(PO3)3 is mixed with CeO2, V2O5 and MnO2, the mixture is melted at 1500° C. in platinum crucibles, cooled and then subjected to several heat treatments in a tube furnace with air supply.
However, it has been shown that the glass ceramics known from the state of the art have insufficient fluorescence properties and cannot imitate the fluorescence properties of natural tooth material to a sufficient extent, in particular under UV light. Dental restorations prepared from such glass ceramics thereby become recognizable as restorations, in particular under the influence of UV light, or are perceived as tooth gaps or defects.